Ultraviolet spectroscopy antioxidants

Polyolefins Aqueous, alcoholic, oily Santonox R (4 4 thiobis-6-tert bicresol) antioxidant Ultraviolet spectroscopy a... 

Generally, methods are based on solvent extraction of the additive followed by analysis for the extracted additive by a suitable physical technique such as visible spectrophotometry of the coupled antioxidant, redox spectrophotometric methods, ultraviolet spectroscopy, infrared spectroscopy, gas chromatography, thin-layer chromatography or column chromatography. In general, direct chemical methods of analysis have not foimd favour. These include potentiometric titration with standard sodium isopropoxide in pyridine medium or reaction of the antioxidant with excess standard potassium bromide-potassium bromate (ie. free bromine) and estimation of the unused bromine by addition of potassium iodide and determination of the iodine produced by titration with sodium thiosulphate to the starch end-point. ... 

Miller and Willis" obtained infrared spectra of antioxidants from polymer films. They compensated with additive free polymer in the reference beam. Infrared spectroscopy is more specific than ultraviolet spectroscopy, but some workers find that the antioxidant level in polymers is too low to give suitable spectra. In-situ spectroscopic techniques are not likely to be of value then, in the analysis of samples of unknown composition. 

Ultraviolet Spectroscopic Procedure. An alternate procedure for determining styrene monomer in polystyrene is based on ultraviolet spectroscopy. Styrene monomer has a strong absorption maximum of 292 nm. Unfortunately, this is subject to interference by aromatic additives, eg. antioxidants, which are often present in... 

METHOD 5 - DETERMINATION OF lONOL PHENOLIC ANTIOXIDANT IN POLYETHYLENE. ULTRAVIOLET SPECTROSCOPY. 

METHOD 7 - DETERMINATION OF 2,6-DITERT-BUTYL-4-METHYLPHENOL AND 4 SUBSTITUTED 2,6-XYLENOL PHENOLIC ANTIOXIDANTS IN POLYPROPYLENE. DERIVATIVE ULTRAVIOLET SPECTROSCOPY. ... 

Derivative ultraviolet spectroscopy is used to determine down to 0.01% 2,6 ditert-butyl-4-methylphenol and 4 substituted 2,6 xylenol phenolic antioxidants in polypropylene. 

Determination of lonol phenolic antioxidant in polyethylene. Ultraviolet spectroscopy... 

Ultraviolet spectroscopy is applicable to the determination of phenolic antioxidants in aqueous and alcoholic simulant liquids and also to one of the fatty simulants, liquid paraffin, recommended by the British Plastics Federation (BPF). Full details of the procedure, which is capable of determining down to 1-2 ppm of Santonox R in the simulent liquids, is given next. With the exception of the 5% citric acid simulent, errors are generally of the order of less than 10% of the determined concentration. Typical recoveries of Santonox R in the 5% citric acid extractant were between 15% of the expected result. 

These surfactants often contain a hindered phenol antioxidant to stabilize the polymer against degradation. Usually, a single antioxidant is present, and it may be determined by ultraviolet spectroscopy. The determination is also conventionally performed by reversed-phase HPLC or by gas chromatography, with or without prior derivatization. Positive identification of the stabilizer can usually be made by direct mass spectrometry. 

Direct methods of analysis such as ultraviolet (UV) absorption, infrared spectroscopy (IR), fluorescence, phosphorescence [13], X-ray fluorescence [14-16] and thermal analysis [17] have been reported. However, these methods generally lack specificity [18]. In Fourier transform IR (FTIR), overlapping bands of other species may interfere with the absorbance bands of the analyte, and in UV analysis the absorbance bands of different antioxidants can be very similar. UV and FTIR analysis are especially useful techniques when an antioxidant system is already known. X-ray fluorescence and elemental analysis are fast and useful techniques for the determination of antioxidants containing phosphorus or sulfur. The measurement of oxygen consumption... 

Soncek and Jelinkova have also used this differential principle to determine in polypropylene two antioxidants (2,6-ditert-butyl-4-methylphenol and 4-substituted 2,6-xylenol) which have virtually identical ultraviolet absorption spectra in the absence of alkali (method 7). The antioxidants can be distinguished in alkaline medium, where 4 substituted 2,6-xylenol forms phenolate readily, thus allowing the utilisation of the bathochromic shift for its determination. The use of derivative spectroscopy reduces light scattering and matrix interferences when extracts from polypropylene samples are measured. 

Methods 17 and 18, respectively, determine Cyasorb UV 531 (2-hydroxy-4-n-octoxybenzophenone) in polyolefins by direct infrared spectroscopy and thin-layer chromatography. Phenolic and organophosphorus type antioxidants do not interfere in these procedures. Method 19 describes an ultraviolet spectroscopic method for the determination of Tinuvin 326 ultraviolet absorber in polypropylene. 

Initially, simple methods such as ultraviolet-visible (UV-Vis), fluorescence or infrared (IR) spectroscopy were proposed in order to estimate the total amount of antioxidants in various food samples. However, coupled methods such as gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography with ultraviolet-visible (HPLC-UV-Vis) or nuclear magnetic resonance detector (HPLC-NMR) and liquid chromatography-mass spectrometry (LC-MS) are employed more to quantify individual tocols or carotens from various corn-based food samples. In this chapter all these methods of analysis will be briefly described. 

Ultraviolet and visible light absorption spectroscopy can be used to identify chromophores (e.g. benzene rings and carbonyl groups) and to determine the lengths of sequences of conjugated multiple bonds in polymers. It also can be used to analyse polymers for the presence of additives such as antioxidants or for detection of residual monomer(s). Additionally, fluorescence and phosphorescence techniques are important in studies of polymer photophysics. 

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